Certain oxidizing agents or oxidants convert alkenes such as unsaturated fatty acids into compounds known as glycols. Glycols are simply dihydroxy alcohols; their formation amounts to the addition of two hydroxyl groups to the double bond. Of the numerous oxidants that caused hydroxylation, two of the most commonly used are cold alkaline potassium permanganate (KMnO4) and peroxyacid such as performic acid. Permanganate oxidation on unsaturated fatty acids usually give vic-diols (cis) in high yield as shown in the equation below. Oxidation or sometimes known as hydroxylation of unsaturated fatty acids will lead to di- and polyhydroxy acids depending on the number of unsaturated present in the acids.

According to the MERCK index, one of the dihydroxy acid, 9,10-dihydroxystearic acid (DHSA) of molecular weight 316.18 and molecular formula of CH3(CH2)7CHOHCHOH(CH2)7COOH is white, odorless, tasteless and lustrous crystal with fatty feel. It is insoluble in water, soluble in hot alcohol or acetone and slightly soluble in ether and has a melting point of 132-136° C. The compound is also reported to find applications in the manufacturing of cosmetic and toilet preparations.
According to U.S. Pat. No. 2,443,280, 9,10-dihydroxystearic acid is produced by conversion of oleic acid with a mixture of hydrogen peroxide and acetic acid as well as catalytic quantities of a strong acid such as sulphuric acid. The hydroxy acetoxy acid developing thereby is regenerated afterwards by soaping with the following decomposition to 9,10-dihydroxystearic acid.
In EP0025940 the production of dihydroxystearic acid is described on the basic of oleic acid, whereby 1 mol of oleic acid is mixed with 4 mole formic acid and to this mixture 1.1 mole of the oxidizing agent hydrogen peroxide is added in the 1 hour process with 50° C. is admitted. The conversion product must be soaped with caustic soda solution and be split afterwards with concentrated hydrochloric acid.
DE4332292 disclosed that hydroxylation of unsaturated carboxylic acids with a hydrogen peroxide and formic acid and/or acetic acid at temperature from 25° C. to 90° C. The reaction required less quantity of catalyst but needs longer response time than EP0025940.
Methods on the production of di- and polyhydroxy fatty acids from mono- or polyunsaturated fatty acid usually in oxidant-catalyst environment such as selenium oxide-tert-butyl hydroperoxide, hydrogen peroxide-tungtic acid, ruthenium and osmium tetroxides. The resultant epoxides are normally hydrolyzed or catalytically opened by adding acetic acid (U.S. Pat. No. 2,443,280) or formic acids (U.S. Pat. No. 4,101,589 and European patent 0025944031). In another U.S. Pat. No. 4,851,593), poly or di-hydroxy fatty acid can be obtained from polymerization of fatty acids in liquid phase reaction at temperature of 260° C. to 343° C. (500° F. to 650° F.), pressure of up to 1000 psi in the presence of a hydrogenation catalyst. These systems however have some disadvantages such as over-oxidation which led to cleavage products, tedious removal of reduced oxidants or the chemicals used were expensive and toxic.
It was also reported that natural hydroxy fatty acids are mostly obtained from the ricinoleic acid present in abundance (˜90%) in castor oil.